1. Field of the Invention
The present invention relates to an apparatus for separating a target material from a sample solution using dielectrophoresis (DEP), and a method of separating a target material and a method of screening an optimum condition for separating a target material using the apparatus.
2. Description of the Related Art
It is well known that a dielectrophoretic force exerts on dielectrically polarizable particles in an non-uniform electric field when effective polarizability of the particles are different from a polarizability of an adjacent medium even if the particles are not charged. The movement of the particles is not determined by the charges of the particles, as is well known in electrophoresis, but is determined by dielectric characteristics (e.g., conductivity and permittivity) of the particles.
The dielectrophoretic force exerting on the particles can be given by:
                              F          DEP                =                  2          ⁢          π          ⁢                                          ⁢                      a            3                    ⁢                      ɛ            m                    ⁢                      Re            ⁡                          (                                                                    ɛ                    p                                    -                                      ɛ                    m                                                                                        ɛ                    p                                    +                                      2                    ⁢                                          ɛ                      m                                                                                  )                                ⁢                      ∇                          E              2                                                          (        1        )            where, FEDP denotes dielectrophoretic force exerting on a particle, a denotes the diameter of the particle, ∈m denotes permittivity of a medium, ∈p denotes permittivity of the particle, Re denotes a real part, E denotes an electric field, and ∇ denotes a del vector operation. As in Equation 1, the dielectrophoretic force is proportional to the volume of the particle, the difference between the permittivity of the medium and the particle, and the square of the strength of the electric field.
                    f        =                  [                                                                      σ                  ~                                p                            -                                                σ                  ~                                m                                                                                      σ                  ~                                p                            +                              2                ⁢                                                      σ                    ~                                    m                                                              ]                                    (        2        )            where f denotes a Clausius-Mossotti (CM) factor, and {tilde over (σ)}p and {tilde over (σ)}m denote composite conductivities of a particle and a medium, respectively. When f>0, positive dielectrophoresis (DEP) is generated and the particle is attracted to a region with a high electric field gradient. When f<0, negative DEP is generated and the particle is attracted to a region with a small electric field gradient.
As shown in Equations 1 and 2, the dielectrophoretic force exerting on the particle can differ depending on the conductivity of the medium, frequency and voltage of the alternating voltage.
An example of a conventional apparatus for separating materials by DEP is disclosed in U.S. Pat. No. 5,569,367 entitled “Apparatus for Separating a Mixture.” The apparatus for separating the mixture by a delay in flow of particles includes a chamber having an inlet and an outlet, an electrode structure installed in the chamber, and a means for applying an alternating voltage. However, the apparatus is for separating a target material using a means which provides a spatially nonhomogeneous alternating electric field in a path along which the target material to be separated flows.
Therefore, in the conventional apparatus, a separating test needs to be repeatedly performed to obtain an optimum conductance value, and voltage and frequency of the current at which the target material is separated. The inventors of the present invention have found that the above-described problem can be solved using a concentration gradient generating unit of an electrolyte while researching into an apparatus that can be used to determine an optimum conductance, and voltage and frequency conditions at which a target material is separated through a single test, and completed the present invention.